The international role of education in sustainable lifestyles and economic development

Improved economic growth and environmental protection are necessary to achieve the United Nations’ Sustainable Development Goals. This study examines the relationship between people’s education levels and sustainable lifestyles in protecting the environment and economic growth, as expressed by the increase in household equivalent income. We conducted an original cross-sectional survey, which yielded 100,956 valid observations in 37 countries. The factors included educational level, sustainable lifestyle with natural resource consumption, and household equivalent income for economic development. We used logit and ordered logit model and applied an ordinary linear regression model after confirming the association between education and income. Our analyses found that higher educational levels were associated with an increase in specific environmentally friendly behaviors and sustainable energy consumption. Individuals in the higher educational level group tended to consume recycled goods, purchase energy-saving household products, conserve electricity, and separate their waste. Additionally, higher levels of education were positively associated with equivalent household income in all 37 countries, indicating better economic development. Thus, our study underscores the importance of improving education at the broad population level to promote economic development and establish cooperative human behaviors necessary to sustain the environment.

www.nature.com/scientificreports/ consumption. In addition, the assessment was conducted in both high-and low-income countries to show heterogenous associations. Furthermore, the role of education on household income and sustainable lifestyles was examined for each of the 37 countries to illustrate economic growth and resource consumption and to show the universal and estimated relationship between them. The empirical analysis was based on an internet survey and face-to-face surveys of the population in regionally and culturally representative countries. People's sustainable lifestyles include recycling goods, electricity conservation, energy-saving products, and waste separation/ avoidance. These types of lifestyles are closely related to environmental issues, and economic growth is related to employment and family income.

Methodology and data
Methodology. Regarding the achievement of sustainable economic development and environmental preservation, we investigated the relationship between sustainable lifestyle behaviors and educational attainment levels (Eq. 1). Referring to the econometric theory 50,51 , when the dependent variable is a binary variable, the logit model and the probit model is believed to be appropriate. Consistent with the previous applied regression model section in Chapman et al. 52 , the logit model is adopted. Equation (1) was constructed as follows: where P iC = prob(S iC = 1) is individual i 's probability of being involved in sustainable lifestyle behaviors. A sustainable lifestyle includes recycled goods usage, electricity conservation, the purchase of energy-saving products, and sorting/reducing waste in the country C . We separately conducted regressions for each sustainable lifestyle behavior. The K denotes a set of educational attainments (senior high school, vocational school, university, and graduate school). The X represents socioeconomic and demographic factors, including age, occupational status (full-time employee, business owner, professional worker, self-employed, homemaker, part-time employee, government employee, student, unemployed, and others), housing status (own, rent, and others), female dummy (yes = 1, no = 0), presence of children dummies (no child, one child, two children, and three or more children). The set of dummy variables D was used to control for country-specific heterogeneity. θ 0 , θ , β and δ are estimated parameters. The error term was denoted as ε.
Human capital is known to play a crucial role in economic development 53,54 , and educational attainment is a key factor for human capital. As the natural environment continues to change, it becomes increasingly important to focus on both economic development and environmental preservation. In this context, sustainable lifestyle behaviors are highly important for environmental preservation, especially at the individual level 9 . As such, this study investigated the relationship between educational attainment and sustainable lifestyle behaviors, aimed at both economic development and environmental preservation. It was found that, if the coefficients for educational attainment are positive, higher educational levels are positively associated with increased sustainable lifestyle behaviors, such as the purchase of energy-saving products.
As the impact of education on sustainable lifestyle may vary country-wise, we accounted for country-specific heterogeneity in the relationship between education and a sustainable lifestyle by running separate regressions for each country. According to the econometric theory 50,51 , when the dependent variable is the scaled dependent variable, the ordered logit model or ordered probit model is appropriate. Thus, based on prior studies, our empirical analysis adopted the model 55,56 . This study used the ordered logit model in the main results and the ordered probit model to verify robustness 51,52,55,56 . For this purpose, we constructed Eq. (2) as follows: in which sustainable lifestyle is denoted as H , with greater numbers indicating better lifestyles for environment sustainability. The year of education variable is denoted as L , which was derived from these educational attainment levels: never attended school = 0, dropped out of primary school = 3, completed primary school = 6, completed junior high school = 9, completed high school = 12, completed vocational school = 14, completed junior college = 15, completed university/college = 16, completed graduate school [master's degree] = 18, and completed graduate school [doctoral degree] = 23). The X represents socioeconomic and demographic variables, including age, occupational status (full-time employee, business owner, professional worker, self-employed, homemaker, part-time employee, government employee, student, unemployed, and others), housing status (own, rent, and others), female dummy (yes = 1, no = 0), presence of children dummies (no child, one child, two children, and three or more children). The values of ρ , γ and η are estimated parameters.
Finally, we constructed Eq. (3) to investigate the impacts of education on economic development, using the ordinary least square model: in which the continuous dependent variable I i is the individual's logarithm of household equivalent income. Variable L i denotes individual i 's education level, with greater numbers indicating more years, (i.e., never attended school = 0, dropped out of primary school = 3, completed primary school = 6, completed junior high school = 9, completed high school = 12, completed vocational school = 14, completed junior college = 15, completed university/college = 16, completed graduate school [master's degree] = 18, and completed graduate school [doctoral degree] = 23). The X again represents socioeconomic and demographic variables, including age, occupational status (full-time employee, business owner, professional worker, self-employed, homemaker, part-time employee, government employee, student, unemployed, and others), housing status (own, rent, and others), female dummy (yes = 1, no = 0), presence of children dummies (no child, one child, two children, and three or more children). www.nature.com/scientificreports/ Parameters a, b , and c were estimated parameters. When educational levels improve the income levels, parameter b is expected to have a positive value and statistical significance. The relationship between the sustainable lifestyle behaviors and educational attainment levels using a logit model and ordered logit model, whereas the association between education and income is explored using ordinary least square models by controlling the individuals' social and demographic background for the 37 nations using the original survey. The strength of the analysis using original survey provides a clear picture of the international viewpoint of this issue with the consistent analysis method.

Data.
To measure the aggregate wealth of society toward sustainability, we conducted an original cross-sectional survey, including 37 nations across six continents, through a third-party survey company in Japan (Nikkei Research Company; interviews were conducted both via the internet and face-to-face). The targeted respondents were selected randomly to match the population's age and gender distribution. Surveys were individually conducted in the investigated countries from 2015 to 2017, yielding 100,956 valid observations. Respondents provided detailed information on their socioeconomic backgrounds, subjective well-being, environmentally sustainable activities, and socioeconomic inequality. The survey was administered in the following countries, arranged by continent, via internet surveys: Face-to-face surveys were conducted in five countries, namely Egypt, Kazakhstan, Mongolia, Myanmar, and Sri Lanka, where internet-based surveys were not feasible.
The above 37 countries contain approximately 73% of the world's population. Detailed observations for each country and additional information on the data collection period are available in the appendices.

Variable selection. Sustainable lifestyle factors and educational attainment.
We selected the following comprehensive activities that are closely related to populational energy consumption and waste recycling. This resulted in a multidimensional range of relevant activities. The questionnaires prompted respondents with the following: "Please select all actions that you have taken these days. Also, please select all activities that you have participated in these days": (1) Purchasing recycled goods.
Respondents rated all items using a binary code: yes = 1, no = 0. Finally, we constructed a comprehensive sustainable lifestyle variable based on an unweighted summation of the above items. This sustainable lifestyle variable thus ranged from 0 to 4 and was expected to capture overall individual activity levels aimed at environmental sustainability, with higher values indicating increased environmental friendliness.
Regarding educational attainment, respondents reported their backgrounds as follows: junior high school or lower, senior high school, vocational school, university, and graduate school. As education is a key factor in economic development [56][57][58][59][60][61][62] , education dummies were used to investigate the relationship between educational attainment and individual-level activities aimed at environmental preservation. Years of education were derived from these educational attainment levels: never attended school = 0, dropped out of primary school = 3, completed primary school = 6, completed junior high school = 9, completed high school = 12, completed vocational school = 14, completed junior college = 15, completed university/college = 16, completed graduate school [master's degree] = 18, and completed graduate school [doctoral degree] = 23.
In the above context, household income was divided by the square root of the number of family members and then transformed into equivalent household income. Amounts were converted into US dollars using the exchange rate as of January 7, 2021. The equivalent scale is the square root of the number of families.
Ethics approval. For the original cross-sectional internet survey conducted by a third-party company (Nikkei Research Company) between 2015 and 2017, the study design was approved by the appropriate legal and ethics review board of Kyushu University. The data were collected with informed consent from participants, according to legal and ethical guidelines. All the methods proceeded in accordance with ethical guidelines and were approved by the ethical committee of Kyushu University.

Results
From the national perspective, the descriptive statistics and sustainability rankings for individual-level lifestyles, including recycling, electricity conservation, use of energy-saving products, and waste separation/avoidance (overall averages of 31%, 62%, 48%, and 61%, respectively), are shown for all 37 countries surveyed (Fig. 1). The rankings are based on the unweighted sum of recycling, saving electricity, buying energy-saving products, and waste separation/reduction. The ranking ranges from Czechia (1st place) to Egypt (37th place). These results highlight the substantial potential for improvement in multiple areas. Examining specific countries showed that China has the world's largest population but ranks 31 among 37 countries. Therefore, improvements targeted at sustainable consumption, waste reduction, and/or energy conservation may constitute a critically important contribution to global environmental preservation. However, results showed that individuals in developing countries were more likely to save electricity and manage waste, which may be reflective of general income constraints.
Overall, the results of this study indicate the positive relationship between educational attainment and a sustainable lifestyle, and the positive association between educational attainment and income is confirmed. As shown in Table 1, notable results were seen. First, university-level or higher education individuals were more likely to engage in sustainable activities. In column (1), the coefficients for senior high school, vocational school, university, and graduate school were 0.028, 0.042, 0.061, and 0.076, respectively; statistical significance was established at 1%, with the reference group being junior school or lower. These results suggest that people with educational attainment have a higher proclivity to consume recycled goods than those with less or no education, even when other control variables remain constant (a magnitude ranging from 2.8% to 7.6% according to educational attainment). As shown in column 4, we found similar results for sorting/reducing waste; in particular, individuals with master's or doctoral degrees were 13.4% more likely to sort/reduce waste compared with those in the lower education group. This may be because those with more extensive education have increased knowledge about the importance of environmental preservation, which influences them to engage in environmentally friendly behaviors.
Regarding electricity conservation and the purchase of energy-saving products, respondents with a university education had the highest level of awareness regarding the benefits of environmentally friendly behaviors pertaining to energy consumption. As shown in column (2), the coefficients for senior high school, vocational school, university, and graduate school were 0.101, 0.127, 0.148, and 0.137, respectively, which indicates that individuals with higher education levels engage in electricity-saving activities at 10.1% to 14.8% higher rates. We found similar results for purchasing energy-saving products, where highly educated individuals were 12.1% more likely to do so. In summary, individuals with university-level education reported more environmentally friendly lifestyles.
Second, higher household income was associated with energy conservation and sorting/reducing waste. As shown in columns (1) through (4) of Table 1, the coefficients for household income were positive and statistically significant. In other words, individuals with higher household incomes were more likely to engage in sustainable  www.nature.com/scientificreports/ lifestyle behaviors, including sorting/reducing waste (highest impact), purchasing energy-saving products, consuming recycled goods, and conserving electricity (lowest impact). Other socioeconomic and demographic factors also influence sustainable lifestyle behaviors. First, women were more likely to engage in these behaviors compared with men (statistically significant at 1%). On average, women were 3.6% more likely to consume recycled goods, 3% more likely to conserve electricity, 0.8% more likely to purchase energy-saving products, and 3.5% more likely to sort/reduce waste. Second, homeowners were more likely to engage in environmental preservation compared with renters and others. Third, occupation status impacted sustainable lifestyle behaviors, as full-time employees and business owners were less likely to conserve electricity compared with unemployed individuals. In addition, business owners and government employees were not likely to sort/reduce waste. Fourth, households with children tended to conserve energy and use environmentally friendly goods.
Based on our logit model (see Eq. (1)), Table 2 shows the relationship between educational attainment and sustainable lifestyle behaviors in higher-and lower-income countries. The dependent variables were use of recycled goods, electricity conservation, purchase of energy-saving products, and sorting/reducing waste. The major independent variables were educational levels, that is, dummy variables comprising senior high school, vocational school, university, and graduate school. The results for higher-and lower-income countries are shown in Panels A and B, respectively.
In both high-and low-income countries, educational attainment had favorable effects on household energy consumption and waste reduction. For example, as shown in column (3), the coefficient for "university" was 0.120, which suggests that individuals with a university-level education were 12% more likely to engage in energy-saving activities when compared with individuals with lower levels of education. Consistent results Table 2. Relationship between education and sustainable lifestyles for high-and low-income countries. Standard errors are shown in parenthesis. Source Authors' calculations. *** p < 0.01, ** p < 0.05, * p < 0.1. Model: Logit model. www.nature.com/scientificreports/ were found for all other educational levels and sustainable lifestyle activities. The coefficients for the education attainment dummies were positive in all the cases (senior high school through graduate school), ranging from 0.025 to 0.120 in higher-income countries and from 0.026 to 0.161 in lower-income countries. This also shows that the positive effects of educational attainment were more pronounced in lower-income countries, which may be related to the condition that improved population education especially facilitates economic development in lower-income countries. Based on our ordered logit model (see Eq. (2)), Fig. 2 shows the influence of increased education on potential improvements in environmentally friendly activities in each surveyed country. The dependent variable was set as the transformed sustainable lifestyle index, which is the unweighted summation of sustainable activities, including the purchase of recycled goods, electricity conservation, the use of energy-saving household products, and sorting/reducing waste. Here, higher values indicate better sustainable lifestyle behaviors. We also analyzed the association between education and economic development for each country via an ordinary least squares model (see Eq. (3) in the Methods section), as shown in panel B of Fig. 2. The value of education was calculated as the years of education, whereas higher education was denoted as more years of schooling.
The results clearly show that higher education levels were associated with increased sustainability behaviors aimed at environmental preservation. In general, this suggests that education is a crucial factor not only for economic development but also for environmental protection. The coefficients for years of education ranged from 0 in Kazakhstan, to 0.82 in Sri Lanka. In 33 of the 37 countries surveyed, higher education levels were statistically and significantly associated with higher frequencies of environmentally friendly behaviors. The said 33 nations include Australia, Brazil, Canada, China, Colombia, Czechia, France, Germany, Greece, Hungary, India, Indonesia, Italy, Japan, Malaysia, Mexico, Mongolia, Myanmar, the Netherlands, the Philippines, Poland, Figure 2. Impact of education on sustainable lifestyles and household income for each surveyed country. Lines denotes a 95% confidence interval. "Filled diamond" denotes the coefficient of schooling by regressing the sustainable lifestyle on schooling and other explanatory variables using an ordered logit model. "Filled circle" denotes the coefficient of schooling by regressing the logarithm of the household equivalent income on schooling and other covariates using an ordinary least square model. Dashed Lines denotes the zero. Source: Authors' calculations. www.nature.com/scientificreports/ Romania, Russia, Singapore, Spain, Sri Lanka, Sweden, Thailand, Turkey, the United Kingdom, the United States, Venezuela, and Vietnam. From the results of the analysis, the preferred education effect was estimated based on the original survey data; for example, China and India have the world's two largest populations, which emphasizes that considerably large environmental improvements can be achieved through increased populational education (respective magnitudes of 0.079 and 0.059, statistically significant at 1%). As mentioned, higher education is positively associated with household equivalent income. The coefficients for years of education were positive, ranging from 0.023 in Canada, the Netherlands, and Sweden, to 0.084 in Chile and Myanmar (statistically significant at 1%). The results also reveal that one year's additional education produced income increases ranging from 2.3% to 8.4%. In summary, national efforts to increase populational education should help achieve better economic development while increasing the overall level of environmental protection. In this regard, our results have important national policy implications for countries working toward the United Nations' SDGs and striving for better economic development.

Discussion
How does education influence individuals' sustainable lifestyles and economic growth from an international perspective? Many scholars and policymakers are now focused on achieving sustainable economic development, while also preserving the natural environment. Therefore, sustainable lifestyle behaviors are crucial, although often difficult to implement. This study clarifies the frequencies of specific behaviors by having conducted a survey spanning 37 nations across six continents, resulting in more than 100,000 international observations. Our subsequent analyses produced some important insights.
First, data from the higher educational institutions shows cities' considerable efforts toward sustainable development owing to the cooperation between higher educational institutions and local governance bodies through employment and innovation 6,63 . Educational attainment played a crucial role in increasing sustainable lifestyle behaviors, specifically in the context of using recycled goods, purchasing energy-saving products, conserving electricity, and reducing/sorting waste. For example, individuals with higher educational levels (e.g., graduate degrees) were 14.8% more likely to engage in electricity conservation behaviors compared to those with lower education levels (e.g., junior high school level). This proved true even when other socioeconomic and demographic factors remained constant. Similar trends were observed for recycling, energy-saving products, and sorting/reducing waste, with magnitudes ranging from 7.6% to 13.4%. This indicates that higher educational levels are positively associated with favorable lifestyle behaviors aimed at environmental preservation. On average, respondents used recycled goods, conserved electricity, purchased energy-saving household products, and sorted/reduced waste at 31%, 62%, 48%, and 61%, respectively. The positive association between educational attainment and a sustainable lifestyle is consistent with previous studies 18, [25][26][27] .
Achieving natural environment sustainability requires fostering a sustainable lifestyle and sustainable consumption production. Higher educational institutions are crucial in promoting better governance and joint city activities between public activities organized through collaboration between local governance bodies and higher educational institutions, while adopting innovation and cooperation 2,6,63 . Consistent with the previous studies, encourage the young generation participate real world associated project improves the social activation for the sustainability.
Second, the relationship between human capital and environment conservation behavior in various countries has been confirmed. For example, the short-tern positive association is confirmed in Pakistan 24 , a long-term positive impact of the human capital on the natural environment conservation is found in China 25 , and both long-term and short-term favorable impact are seen in South Africa. In this study, comparing the human capital increase in higher and lower-income countries revealed that education substantially affects sustainable lifestyle behaviors. More favorable effects were seen in lower-income countries: individuals with higher levels of education were 9% to 16.5% more likely to engage in sustainable energy conservation and waste sorting/reduction activities. These results are consistent with previous studies that focused on pro-environmental behavior 10,11 . In this context, improved populational education is expected to help sustain natural resource consumption, especially in lower-income countries.
Third, based on the individual-level microdata from each country, higher education levels were found to be associated with increased sustainability behaviors aimed at environmental preservation. This result suggests that education is a crucial factor for economic development and environmental preservation. We found a preferred education effect in 32 of 37 nations, including China and India, which have the world's first and second largest populations, respectively; this shows that profound effects can be achieved by enhancing education at the populational level.
Furthermore, we found a positive relationship between educational attainment and increased income in all 37 nations studied. The results reveal that one additional year of education improved annual incomes by 2.3% to 8.4%. This finding is consistent with previous studies, such as Rahim et al. 22 , that disclosed that human capital and natural resources contribute to a positive impact on economic growth. By contrast, the positive relationship between economic growth increases the burden on natural resources; however, no causal relationship is confirmed. In South Africa, the unfavorable casual impact of the economic growth on the natural environment is seen in Iorember et al. 26 . In India, the negative u-shaped pattern between economic growth and the natural environment burden is confirmed 27 . Overall, as there are clear positive impacts on environmental preservation, large-scale efforts to improve populational education may enhance sustainability practices at the societal level.
As indicated by the results, the policy implications for all the investigated countries are as follows. First, widespread education should increase the frequency at which individuals engage in activities aimed at environmental preservation, which is critically important for responding to current changes in the natural environment. This corroborates evidence produced in previous studies on the need to reshape human behavior toward more  9 . Second, economic development is closely associated with daily household life. In this case, economic development and natural preservation are core, intertwined issues, both in the short-and long-term. Our results clearly show that education is a crucial factor for not only economic development but also environmental preservation; that is, higher education is associated with more environmentally friendly behaviors at the individual level. This effect was more pronounced in lower-income countries, including those with substantially large populations, such as China, India, and Indonesia. In summary, policymakers may take these factors into consideration by implementing policies aimed at increasing population education; this will contribute to both better economic development and environmental conservation, as education clearly increases the rate of sustainable behavior. To produce sustainable educational institutes, universities could offer more encouragement to the younger generation involved in project solving of real-world issues. This study clarifies the relationship between educational level and sustainable lifestyle, as well as household income, from an international perspective. However, this study is subject to some limitations. First, this study used the original internet and face-to-face survey data collected by Nikkei Research. A focus on internet users in research is more likely to target those with better education or higher income, which might result in a sample selection bias in the regression analysis. We attempted to conduct face-to-face surveys in some nations to perform robustness checks, and we found the results to be consistent with the sample derived from the internet survey done by Nikkei Research. However, the main results might still exhibit a sample selection problem; therefore, future studies are encouraged to employ comprehensive datasets to investigate this issue. Second, we examined the relationship between education and economic growth as well as sustainable lifestyles in this study, considering cross-sectional international survey data from 37 nations. Future studies could further explore the causal effect of education on economic growth and sustainable lifestyles. Furthermore, although this study confirmed a positive relationship between education and sustainable lifestyles as well as household income, the results do not explain whether it is a casual effect; this could be examined in future studies. This study uses original internet and face-to-face data derived from 37 nations during 2015 to 2017. The original survey collected detailed individual level environmental conservation attitudes, pro-environmental behavior, and socio-economic and demographic background, allowing this study to investigate the relationship between education, economic growth, and environment conservation from individual perspectives. The results of this study can provide insightful evidence to the field of sustainability development research. However, the data were collected in about 2016, and most of the data appear relatively old and might be subject to estimation bias caused by the technological gap in different time periods. Therefore, using more recent and comprehensive datasets in the future is recommended for investigating the association between economic growth, environmental conservation, and education.

Conclusion
This study employed a large-scaled original internet and face-to-face individual survey to show the impact of educational attainment on sustainable development. The original survey is derived from 37 nations with 100,956 valid observations collected using individuals' sustainable lifestyle as well as socio-economic and demographic background. We confirmed the relationship between educational attainment and household income by country and explored the association between education and sustainable lifestyle. The results are expected to provide insightful evidence to policymakers.

Data availability
The data is available upon reasonable request to the authors Xiangdan Piao or Shunsuke Managi.